Good — Progression Through Skill
If there's one good thing to say about Sumioni: Demon Arts—and I stress the "if"—it's that the game's difficulty tailors itself to your skill. In the easiest path through the game, it's only six levels long and can be beaten in less than a half hour. However, if you are able to beat certain levels quickly while minimizing the damage you take, you will find yourself on a harder path with new enemies and more levels overall.
Bad — You Got Your Bullet Hell Game in My Action Game
Sadly though, the main way Sumioni increases its difficulty is by simply filling the screen with more and more enemies and bullets. Soon it looks and feels more like a bullet hell game than an action/platformer. While this is not inherently a bad thing, the fact that your character has only a melee weapon and the bosses have insane amounts of life makes each moment spent dodging a frustrating bore.
Bad — Déjà Vu All Over Again
Levels in Sumioni come in three flavors: 1) "Escape giant monster that is chasing you" 2) "Survive the endless waves of enemies until time runs out" and 3) "Kill the enemies as you go left until you fight a giant tower"—which is by far the most popular. Normal enemies die in a single hit so only their numbers make them any kind of challenge. Worse yet, the bosses (read: giant towers) are nearly identical across each difficulty as well; all that changes is how many bullets they spam.
Bad — Bad Touch! I Need an Adult!
Perhaps everything else would level out if it weren't for the fact that as much as you're fighting enemies and towers, you're fighting the controls as well. The platforming aspect of Sumioni comes from your ability to draw ink platforms using the Vita's touchscreen. While this generally works, touching the screen also makes your character attack. And though this doesn't seem like a problem at first glance, several levels are filled with enemies that explode when touched—or attacked—as the case may be.
Bad — Sumie Style Makes for a Bland, Color-Starved Game
Sumie traditionally means black ink on a gray-ish rice paper with occasional red highlights. Frankly put, this color palate does not make for a visually appealing game. The worst thing is we have already seen that games created in sumie style can look beautiful. By abandoning the limited sumie color pallet, Okami—and its successor Okamiden—created a sumie style world filled with vibrant colors. Sumioni looks appallingly bland in comparison.
What has been hailed as the Vita's most artistic title is nothing of the sort. Instead it's a mediocre platforming/adventure game that squanders its intriguing concept in every possible way. I truly hope this is not the last sumie-inspired game we see on the Vita or any other system. After all, it's not the art style that failed Sumioni, it's Sumioni that failed the art style.
Update: Removed section with incorrect information. Thanks commenters for pointing it out.